The present invention relates generally to digital communication networks, and more specifically, to methods and systems for efficiently transporting Fibre Channel client data over a SONET/SDH network path.
SONET/SDH and optical fiber have emerged as significant technologies for building large scale, high speed, Internet Protocol (IP) based networks. SONET, an acronym for Synchronous Optical Network, and SDH, an acronym for Synchronous Digital Hierarchy, are a set of related standards for synchronous data transmission over fiber optic networks. SONET/SDH is currently used in wide area networks (WAN) and metropolitan area networks (MAN). A SONET system consists of switches, multiplexers, and repeaters, all connected by fiber. The connection between a source and destination is called a path.
One network architecture for the network interconnection of computer devices is Fibre Channel, the core standard of which is described in ANSI (American National Standards Institute) X3.230-1994. Arising out of data storage requirements, Fibre Channel currently provides for bi-directional gigabit-per-second transport over communication networks in Fibre Channel frames that consist of standardized sets of bits used to carry data over the network system. Fibre Channel links are limited to no more than 10 kilometers.
New standards and protocols have emerged to combine the advantages of the SONET/SDH and Fibre Channel technologies. For example, it is sometimes desirable to link two SANs (Storage Area Networks), which operate with Fibre Channel protocol, over a MAN (Metropolitan Area Network), or even a WAN (Wide Area Network), which typically operates under SONET or SDH standards. This extension of Fibre Channel from 100 kilometers to over several hundred, or even thousand, kilometers, is made by mapping Fibre Channel ports to a SONET/SDH path for transport across a SONET/SDH network. One way to perform this function is to encapsulate Fibre Channel client data frames into transparent Generic Framing Protocol (GFP-T) frames and then map the GFP-T frames into SONET/SDH frames for transport across the SONET/SDH network. In this manner two Fibre Channel ports can communicate with each other over a SONET/SDH network as though the intervening network links are part of a Fibre Channel network. The Fibre Channel ports remain “unaware” of the SONET/SDH transport path.
Fibre Channel protocol handles the flow of Fibre Channel data frames with buffer credit management. Two communicating Fibre Channel nodes initially report to each other on the amount of space (credits) in each port's buffer available to receive Fibre Channel frames from the other port. Once the credits are established, a transmitting node sends its frames and uses its credits. Upon receiving the frames, the receiving node sends back some acknowledgment signal so that the credits of the transmitting node are replenished for more transmission. In end-to-end flow control, the frame source and frame destination nodes are the two nodes; in buffer-to-buffer credit flow control, the two nodes on opposite sides of a link are the two nodes.
Fibre Channel systems are sensitive to frame loss and, despite the transparency with encapsulating Fibre Channel frames in GFP-T envelopes for transport over a SONET/SDH network, there is the possibility of glitches or errors in the a SONET/SDH network. The result is reduced throughput and/or extended failure times, which is contrary to the high-speed nature of Fibre Channel.
The present invention permits Fibre Channel ports to restore the apparent link between the ports quickly from failures in the SONET/SDH transport path without undue complexity.